This study plans to use a novel molecule (MK591), which has already been tested extensively in other human diseases, to investigate the impact of leukotriene biosynthesis inhibition on the acute (and eventually the chronic) course of active glomerulonephritis in humans. The investigators hypothesize that short-term (4 day) inhibition of leukotriene biosynthesis in acute glomerulonephritis will result in an improvement in GFR and a reduction in proteinuria.